A lithium-ion battery (Li-ion battery) is a battery in which lithium ions move between oppositely charged electrodes to generate electricity.
The corrupting (malfunctioning) of a Li-ion battery, such as by short circuiting within the battery, is known to be capable of producing a runaway thermal reaction that vaporizes combustible components within the battery, especially from the electrolyte separating each anode from each cathode of the battery. Combustion of the battery involves ignition of the combustible vapors, especially upon reaching oxygen present in air that comes into contact with the combustible vapors, either within the battery pack case within which the battery is housed or exterior to the battery pack from which the combustible vapors escape.
In an effort to stop the flow of electricity to the compromised battery, battery packs have been equipped with fusing that stops electricity flow upon an excessive rise in temperature caused by the run-away thermal reaction within the battery.
Because the electrical approach has not always been effective in abating the combustion, various other techniques have been tried.
U.S. 2011/0177366 discloses the formation of the case of the battery pack as a laminate of (i) a heat conductive layer of metal or resin having high heat conductivity such as an engineering plastic and (ii) a heat absorbing layer of resin materials, ceramic materials or inorganic materials. Layer (i) forms the outside of the case and layer (ii) forms the inside of the case, so that the heat absorbed by layer (ii) is conducted away from the interior of the batter pack case by layer (i). Fluorocarbon resin is disclosed as a possible material for layer (ii), and polytetrafluoroethylene (PTFE) is disclosed as an example of resin having superior heat resistance. The PTFE heat absorbing layer is disclosed to contain 20 to 70 parts by weight of particulate material called material B dispersed therein, and the PTFE is disclosed to have excellent binding property. The function of the particulate material B in layer (ii) is to undergo a heat decomposition reaction, which absorbs heat and expands the layer (ii) to form an insulating layer to protect electronic devices outside the battery pack case. Sodium hydrogen carbonate and aluminum hydroxide are disclosed as examples of material B. As apparent compensation of the insulating effect of the insulating layer (ii) after heating, the battery pack is also provided with a sinusoidal conduit 25 (FIG. 2) for allowing escape of hot gases from the interior of the battery pack case and air cooling this gas as it flows along the length of the conduit. The approach of this patent publication is to try to avoid emission of a high temperature inflammable gas from the inside of the battery pack by limiting the temperature rise within the battery pack and cooling the gas escaping from the battery pack.
U.S. 2009/0176148 discloses the immersion of batteries into a container filled with a heat transfer fluid, and containing a heat exchange at least partially filled with the heat transfer fluid, wherein the fluid is a liquid or gas, such as water, glycols, perfluorocarbons, perfluoropolyethers, perfluoroamines, perfluoroethers, silicone oil and hydrocarbon oils and the heat exchanger contributes the removal of heat from the immersed batteries. In another embodiment, the heat transfer fluid is a hydrofluoroether that has a low boiling temperature, e.g. less than 80° C. or even less than 50° C., the vaporization of this fluid contributing to the heat removal from the immersed batteries. A disadvantage of this approach to improving the safety of batteries, i.e. combustion abatement, is the reliance on gas and/or liquid as the transfer fluid. Gas or liquids within the battery pack case are prone to escape upon any opening being formed in the case, such as by subjecting the case to an impact.
U.S. 2010/0047673 discloses filling the space between the battery pack case and the batteries containing within the case with a nonflammable filling material so as to exclude air from the inside of the case. In one embodiment, liquid or gas is used as the filling material and either contained within a polypropylene bag or absorbed into a high polymer to provide a gel-like material. Example 12 discloses the preparation of a filling material by kneading 90 w % magnesium hydrogen carbonate powder that releases carbon dioxide when overheated, with 10 wt % PTFE having a bonding effect in a mortar, the resulting mixture then being molded into pellets, which then becomes the filling material within the battery case. One skilled in the art knows that for the PTFE to have a bonding effect, the PTFE must be the fine powder type, made by aqueous dispersion polymerization, followed by coagulation of the dispersed PTFE particles, the resulting coagulum being called the fine powder type of PTFE. This PTFE fine powder, prior to sintering, fibrillates when subject to shear as occurs in mixing in a mortar. The fibrils making up the fibrillated PTFE act as a bonding agent for particulate material such as the magnesium hydrogen carbonate used in Example 12. It is clear that in this application, the PTFE is used for its bonding ability, with the magnesium hydrogen carbonate being the fire suppressant in the filling material.
There is a still a need for an effective way of abating combustion by a Li-ion battery.